Human vocal folds, commonly known as vocal cords, help to regulate breathing, phonation and swallowing. The vocal cords are paired mucous membranes located in the larynx, which connects the pharynx and the trachea. Ordinarily, the vocal cords help produce speech by vibrating while a person exhales. The production of speech requires the vocal cords to be in close proximity to each other and vibrate as air is exhaled, thereby imparting oscillations (sound waves) into the passing air. The vocal cords help to regulate breathing by remaining open while a person breathes in or out and closed when a person is not breathing. They also remain closed during swallowing, helping to prevent food passing into the trachea.
Paralysis or impairment of a single vocal cord (unilateral vocal cord paralysis) can negatively affect a person's ability to breath, speak and swallow, and can be traced to neoplastic, iatrogenic, neurologic (Parkinson's, multiple sclerosis), congenital, or idiopathic causes, as well as to mechanical trauma. One specific cause is impairment of one of the recurrent laryngeal nerves, which help control the vocal cords. Vocal cord paralysis can occur at any age, though most commonly in older patients, and in both men and women. Paralysis of the left vocal cord is more common than paralysis of the right vocal cord, a fact attributable to the differences between the left and right recurrent laryngeal nerves. Another important cause of vocal cord impairment that is often overlooked is loss of vocal cord bulk, termed presbylaryngis, due to atrophy of the mucscular tone in the elderly population. Glottic cancer in which either surgical intervention through a cordectomy or with radiation treatment can also result in a decrease of vocal cord volume.
One known method of treating unilateral vocal cord paralysis is to medially displace the paralyzed vocal cord, thereby permitting it to approximate the functional vocal cord during phonation in a procedure sometimes referred to as medialization thyroplasty type II. One known method of doing so is cutting an opening in the thyroid lamina (which is made of cartilage), and mounting an implant on the cartilage in a way that pushes the non-functioning vocal cord medially, into the patient's glottis, and closer to the functional vocal cord. These methods can increase an individual's ability to speak and regulate breathing and prevent aspiration during swallowing by allowing the functional vocal cord to be substantially close the larynx.
Thyroplasty implants are known in the field. U.S. Pat. No. 5,358,522 to Montgomery, et al., describes an implant having a tiered base for anchoring in a window cut through the thyroid lamina and a projecting member for causing medial displacement of a vocal cord. Boston Medical Products Inc. markets thyroplasty implants made of soft silicone material under the Montgomery name, similar to those disclosed in the '522 patent. U.S. Pat. No. 5,549,673 to Beale describes an implant designed to be inserted through an opening in the thyroid cartilage, and which has a holding portion which facilitates insertion and allows the implant to be held in place by a shim. The literature also describes a triangular implant attached to a plate by a screw, and which is adjustable in one direction by turning the screw. Another known implant is an implantable balloon designed to be inflated with silicone to medialize the paralyzed vocal cord.
While these implants provide some benefits, they have several drawbacks. For example, in some cases they require proper sizing of the implants (such as by carving the implant itself) in order to be effective. Sizing of the implant is often determined during a procedure by implanting a test device and having the patient speak, thereby determining in real-time the benefits provided to the patient's phonation, but not assessment of aspiration. This method can increase the time required to complete a procedure and thus lead to increased trauma and edema in the patient's vocal cords, thereby reducing the effectiveness of the real-time testing (making it hard to discern to what degree improvements in phonation are due to the implant vs. due to edema). Further, balloon implants suffer from the drawback that their final shape is determined by the shape of the balloon itself: their shape is less customizable to individual patients. Finally, existing implants suffer complications such as persistent dysphonia, airway obstruction due to implant extrusion into the airway, and implant migration. In addition, commercially available implants may not be capable of closing large posterior gaps between the vocal cords, thereby necessitating an additional surgical procedure, an arytenoid adduction, to prevent aspiration. Accordingly, implants which can reduce trauma and edema that results from “trial and error” fitting of the various implants during the procedure, and implants with increased adjustability and tissue biocompatibility would be beneficial to prevent or reduce the aforementioned associated complications.